A number of disclosures such as those set forth in U.S. Pat. Nos. 3,577,330; 3,668,081; 3,883,411 and Canadian Pat. No. 955,195 deal with cathode mandrels for electrodeposition of nickel. In general these disclosures teach use of mandrels made of stainless steel, titanium and aluminum which are sand blasted to defined surface finishes in terms of microinches (as measured by a profilometer) in interrelationship with internal stress levels of nickel deposited on such mandrels.
The teachings of these prior patents have not been entirely successful when carried into practice on a commercial scale. The object of these teachings is to provide mandrels which cause adherence of nickel deposits during electrodeposition and ready removal of the deposits when the deposition is finished. The problem which arises in commercial production is that it is not possible to maintain the internal stress level of electrodeposited nickel constant over any extended periof of time. For reasons both known and unknown the electrolyte composition may vary from day to day and from week to week. These variations can be meaningless in terms of purity and quality of product produced but can be highly significant in terms of adherence of the deposited nickel to the mandrels. Under conditions of low internal stress, a high degree of mandrel roughness will cause too much adherence and it will be difficult to remove the electrodeposited nickel from the mandrel. On the other hand, under condition of high internal stress, too little mandrel roughness will be ineffective in terms of adherence of the deposited nickel to such mandrels.
What is needed then for commercial use are mandrels surface finished in such a way as to be broadly tolerant of unavoidable variations in internal stress of nickel electrodeposits.